Guinea. Economic analysis

Guinea is the world leader in aluminum ore reserves, both among developed and developing countries. More specific information on Guinea's bauxite resources is often contradictory. In the course of prospecting works the total bauxite reserve estimations kept growing. Now, according to different authors, they range from 18 to 25 bln tons for Guinea. More than 150 bauxite formations were discovered; all of them are located in the bauxite-bearing Futa Jallon-Mandingo province. Besides that, bauxite layers are also known to occur in the mountainous regions of eastern Guinea - Niandan-Banye ridge and other locations. All the explored bauxite formations are related to flat-topped upland at hypsometrical levels ranging from 150 to 1300 meters. The ores make up the upper part of the residuum, 30 to 40 meters thick, developed on various sedimentary-terrigenous, metamorphic, intrusive, and other rocks. The flat sheets usually repeat the configuration of the flat-topped mountains' and hills' crests. The thickness of the producing horizon varies between 6 to 12 meters, sometimes thicker. The overburden never exceeds a meter and a half; at times there's no overburden at all. Mineralogically, bauxites are gibbsitic with a possible admixture of boehmite. High iron content and relatively low silica content is a characteristic. In the row of workable bauxite deposits apart stand lateritic eluvial (residual) formations and re-deposited layers, as well as lateritic-sedimentary ones. Eluvial deposits can be found on the flat-topped upland and are related to the upper part of lateritic residuum. In the sector, transition is gradual between the unweathered fresh parent rock and all structural clays and bauxites. The ores are distinguished by high alumina content (40-60%) and low silica content (1.5-3.0%). Re-deposited bauxites make up workable deposits in the form of diluvial-proluvial aprons. Some of the re-deposited bauxite layers seem to have no visible connection with the eluvial deposits. Lateritic residua of sedimentary rocks and, possibly, dolerites were the source of the bauxite formations of this kind. By nature of the rock waste, brecciform, conglomerate and gravelstone subgroups are distinguished. Oolitic-pisolitic bauxites are also possible here, although they don't usually make up major formations. The complex of rocks that produces a bauxite-bearing rock mass must have either a free oxides zone of the eluvial crust, or a diluvial-proluvial cover above. Bauxite-bearing mass covers the surfaces of uplands and their gentle slopes with a vast hood. The rock mass's lower end coincides with a rather sharp division line between bauxites of the free oxides zone and clayey content of the transition zone. The inside structure of the ore mass is not overly complicated. Whatever the case, it is always made up of bauxites, allites and, less importantly, iron ores. In terms of chemical composition, however, bauxites are vastly diverse. Their moving around both horizontally and vertically is responsible for this motley choice. All the rocks in the bauxite-bearing mass are marked by a variety of structural and detritus differences. The content is the same, the difference lies in the quantitative proportion of every mineral component in the rock's structure. A distinctive characteristic of the section is the presence of quartz in the cementing mass, and that the quartz's ratio may turn out a substantial one. Usually, this is quite typical for the lower part of the bauxite-bearing mass section. In the interval of the underground water oscillations rock density may become lower, and this leads to friability differences. As for the age, the bauxite formations date back to Cretaceous - Pliocene - low Quaternary periods time span. This bauxite profile is relevant not only to the description of one particular deposit, but all bauxite deposits on Guinean territory. Nowadays, bauxites in Guinea are being recovered in three quarries: Debele, Kimbo, and Sangaredi.
Sangaredi deposit is located on a table upland with true elevation of 220-240 meters, its area is 12 sq. km. The ore body is up to 40 meters thick. It comprises sandstone, gravelstone, conglomerate, pisolitic and clayline bauxites of lateritic-sedimentary genesis. Minel composition of the upper part of the deposit is mainly gibbsitic, while the lower part is gibbsite-boehmite. In general, Sangaredi ores stand out for their excellent quality. Alumina content in almost all the bauxites is over 60%, with low silica (0.5 to 1.6%) and iron (1.5 to 6.8%) ratios. Ore reserve - 170 to 190 mln tons.
Debele deposit is related to the upland, 490-562 meters high and 0.5 sq. km. in area. Bauxite horizon occupies the upper part of the lateritic residuum, with developed rocks of the Silurian period. The thickness of the producing horizon ranges between 4 and 13 meters. The ores are of high and medium quality. Alumina content varies between 44% and 63%. Explored reserves by the beginning of utilization were assessed at 44.4 mln tons.
Certain deposits, by their total reserves, can only be referred to as unique. For instance, Sintiouru formation is said to hide 501 mln tons with average aluminum content of 46.6%, and Dabola-Tagyurate formation - 431 mln tons and 48% respectively.

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